In an image forming apparatus (e.g., an MFP), a sheet finishing apparatus is provided adjacent to the MFP at a post stage in order to apply finishing to sheets subjected to image formation. The sheet finishing apparatus is called a finisher. The finisher staples or sorts sheets sent from the MFP.
The finisher includes lateral alignment plates that control the position in the width direction of sheets. The finisher aligns the sheets in the width direction and conveys the sheets to a stapler. The stapler staples the sheets. The lateral alignment plates are used as well when the sheets are sorted and discharged.
Sheets discharged from the finisher are discharged from a discharge port to a stack tray. The sheets are sometimes deformed or curled. If the sheets are deformed or curled, the trailing end of the sheet discharged to the stack tray remains in the discharge port, obstructs the discharge of the following sheets, and causes a jam and an alignment failure.
If the leading end of the sheet discharged to the stack tray is curled in a downward direction, the sheets hit the stack tray or the leading end of the sheet is rounded to cause a jam and an alignment failure.